In the lithographical process for silicon wafers using photomask, after the project objective of the lithography machine being radiated by the laser beams from the lithography machine for a long time, the thermally induced mechanical deformations of the project objective may occurs. Generally, the project objective comprises multiple lenses. The heat absorbed in the lens on the top of the project objective is different with that absorbed in the lens at the bottom of the project objective, and such heat variation may induce different deformations in the top lens and the bottom lens, so as to cause magnification error during the exposure process. Therefore, the alignment precision between silicon wafers or between lots may be reduced in the continuous operation of the lithography machine. Furthermore, the heat from the laser beams during the lithographical process will be accumulated over the exposure time and the alignment errors between wafers or lots may not be avoided.
The Chinese patent No. 101609262 discloses a temperature control device of a projection object lens of a lithography machine. The temperature control device comprises at least one water sleeve which encloses the projection object lens, at least one temperature sensor disposed adjacent to the projection object lens, a flow distributing and collecting plate, a circulating water control unit and a temperature control unit of the projection object lens. The water sleeve comprises a water sleeve body and a water pipe double-spirally enwound on the outer wall of the water sleeve body; the temperature sensor is used for detecting the temperature of the projection object lens of the lithography machine; the flow distributing and collecting plate is connected with the water pipe of the water sleeve through a flow distributing and collecting pipe to provide circulating water for the water pipe of the water sleeve and receive recirculation water in the water pipe of the water sleeve body, and the flow distributing and collecting pipe is provided with an adjusting valve used for controlling the flow rate of the circulating water in the water pipe; the circulating water control unit controls the temperature of the circulating water and provides circulating water for the flow distributing and collecting plate through a transmission pipe; the temperature control unit of the projection object lens is used for receiving the temperature of the projection object lens detected by the temperature sensor and adjusting the temperature of the circulating water provided by the circulating water control unit and the opening degree of the adjusting valve according to the temperature of the projection object lens.
However, when the temperature of the bottom of the projection object lens is greatly below that of the other areas of the projection object lens, or the temperature of the projection object lens grows non-linearly from bottom to top, it may require a long time to realize the integral temperature uniformity of the projection object lens. In addition, the structure of the temperature control device is complicated which may bring inconvenience in installation and maintenance.